<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* :root {
      font-size: 16px;
    } */


    .p1 {
      font-size: small;
      /* font-size: smaller; */
    }

    .p2 {
      font-size: medium;
    }

    .p3 {
      font-size: large;
      /* font-size: larger; */
    }

    .p3 b {
      font-size: smaller;
    }
  </style>
</head>

<body>
  <p class="p1">this is p1 small</p>
  <p class="p2">this is p2</p>
  <p class="p3">this is p3
    <b>smaller</b>
  </p>

</body>

</html>